Spindle motor for hard disk drives

ABSTRACT

A spindle motor for use in hard disk drives having a base plate, a stationary shaft, a rotationally driven rotor, and a bearing system rotationally supporting the rotationally driven rotor. The shaft is fixedly mounted on the base plate. The base plate includes a drilled hole for insertion of a portion of the shaft such that this shaft&#39;s portion and the inner surface of the hole define a joint length l, when this portion is pressed into the drilled hole. The shaft has at least one notch located along the shaft&#39;s circumference and interrupting the joint length l.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims all rights of priority to German PatentApplication Serial No. 201 19 716.2, filed Dec. 5, 2001 (pending).

BACKGROUND

[0002] The invention relates to a spindle motor for memory devices suchas hard disk drives.

[0003] Conventional spindle motors for hard disk drives include a baseplate or a base flange, a shaft, and a bearing system for rotationallysupporting a motor's rotor driven by an electromagnetic force. Thebearing system may be structured as a rolling bearing system or ahydrodynamic sliding bearing system.

[0004] In a conventional spindle motor having a stationary shaft, theshaft is firmly connected to the base plate or the base flange by meansof a press-fit connection. To accomplish the connection, the base plateor the base flange features a drilled hole of a predetermined diameterand a predetermined length. One end of the shaft is pressed into andsecured within the drilled hole. The outside diameter of the shaft istypically slightly larger than the inside diameter of the drilled holeof the base plate. This surplus is selected so as to ensure a minimaladhesive dimension, i.e., a certain adhesive strength, along the entirelength of the joint. On the other hand, the surplus is selected toensure that a maximum adhesive dimension is not exceeded. An excessivesurplus would lead to an unacceptable strain on the components.

[0005] The greater the surplus and joint length, the higher is thepress-in force required to join together the base plate and shaft. Ifthe surplus or the joint length is reduced, adhesive strength may becometoo small. Increasing the surplus or joint length may result in damageto the components during the press-in procedure.

BRIEF SUMMARY

[0006] In general, in a first aspect, the invention features a spindlemotor for use with hard disk drives having a base plate, a stationaryshaft, a rotationally driven rotor, and a bearing system rotationallysupporting the rotationally driven rotor. The shaft is fixedly mountedon the base plate. The base plate includes a drilled hole for insertionof a portion of the shaft such that this shaft's portion and the innersurface of the hole define a joint length l, when this portion ispressed into the drilled hole. The shaft has at least one notch locatedalong the shaft's circumference and interrupting the joint length l.

[0007] The provided construction of the spindle motor results in thereduced press-in force needed to insert the shaft into the drilled holein the base plate. This is attributable to the fact that the effectivejoint length is shortened by the notch in the shaft, and that the shaftand base plate are only connected in the two joint segments above andbelow the notch.

[0008] Nevertheless, a very favorable retention effect and a firm pressfit of the shaft in the base plate can be achieved, since a largersurplus can be used in the remaining joint segments.

[0009] Consequently, the shaft can be connected to the base plate in amanner that is less damaging to the components.

[0010] In a preferred embodiment of the invention, the outer diameter ofthe shaft in proximity to the notch is substantially smaller than theinner diameter of the drilled hole in the base plate. Consequently, theshaft does not contact the inside wall of the drilled hole in the baseplate in the area surrounding the notch, and no adhesive forces arecreated in this area. This facilitates the insertion of the shaft.

[0011] The notch preferably continues along at least half of the jointlength, which nevertheless makes it possible to achieve a sufficientlyfirm connection.

[0012] Production of the notched shaft requires only a minimal increasein cost when compared with the production of a conventional shaft. Thenotched shaft may be made by being turned on a lathe, and issubsequently ground to size with a high degree of precision. Anyexisting chips or burrs in the transition area between the outerdiameter and the point of insertion are eliminated by the polishingprocess.

[0013] The invention provides a design of a spindle motor for hard diskdrives, where a small amount of press-in force is needed to jointogether the shaft and the base plate, but where a high degree ofadhesive force is also achieved.

[0014] The above aspects, advantages and features are of representativeembodiments only. It should be understood that they are not to beconsidered limitations on the invention as defined by the claims.Additional features and advantages of the invention will become apparentin the following description, from the drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The invention is illustrated by way of example and not limitationand the figures of the accompanying drawings in which like referencesdenote like or corresponding parts, and in which:

[0016]FIG. 1 is a cross-sectional view of a spindle motor for hard diskdrives constructed in accordance with the preferred embodiment of thepresent invention.

[0017]FIG. 2 is an enlarged cross-sectional view of the end of the shaftto be connected to the base plate, in accordance with the preferredembodiment of the present invention.

[0018]FIG. 3 is an enlarged cross-sectional view of the drilled hole ofthe base plate.

[0019]FIG. 4 is an enlarged cross-sectional view of the formed press-fitconnection between the end of the shaft and the base plate, inaccordance with the preferred embodiment of the present invention.

DETAILED DESCRIPTION

[0020] As shown in FIG. 1, in accordance with the preferred embodimentof the present invention, a spindle motor is provided having a baseplate 1 and a shaft 2 firmly connected to the base plate. A rotor 5 isrotationally mounted on shaft 2 by means of a bearing system 3,preferably structured as a hydrodynamic sliding bearing system. Bearingsystem 3 is protected from the exterior by a lid 4. Rotor 5 is equippedwith rotor magnets 6 located along rotor's inner circumference. Rotormagnets correspond to a plurality of electrical coils located on a fixedstator 7 arranged on the base plate 1. Rotor 5 is actuated by analternating electric field generated by the electrical coils interactingwith the rotor magnets. A contacting unit 8 is provided to supply anelectrical current to the electrical coils of stator 7.

[0021] As shown in FIG. 3, base plate 1 features a cylindrical drilledhole 9 with a predetermined constant inner diameter. One end of shaft 2is accepted in a forced fit into the cylindrical hole 9. An outerdiameter of shaft 2 is slightly larger than the inner diameter of thecylindrical drilled hole, so that the shaft's end is frictionally andfixedly engaged in base plate 1 once the components have been joinedtogether.

[0022] As shown in FIGS. 1 and 2, the theoretical length l of the jointbetween the cylindrical hole 9 and the shaft's end is, according to theinvention, interrupted by a notch 10, effectively creating an upperjoint segment 11 and a lower joint segment 12. The outer diameter ofshaft 2 within the boundaries of the notch is substantially smaller thanthe predetermined outer diameter of the upper and lower joint segments.The outer diameter of the notch is likewise substantially smaller thanthe inner diameter of the cylindrical drilled hole 9. Thus, theeffective length of the shaft-base joint is shortened by the notch inthe shaft resulting in the shaft and base plate being only connected inthe two joint segments above and below the notch.

[0023] In one preferred embodiment, the length s of notch 10 correspondsto approximately half of the theoretical joint length l. In another,most preferred embodiment, the length s is preferably greater than halfof the joint length l.

[0024] As shown in FIG. 4, when the shaft's end is pressed into thedrilled hole 9 of the base plate 1, the press fit connection isestablished only along the upper and lower joint segments (11 and 12).No adhesive connection is formed in the area surrounding notch 10.

[0025] When a spindle motor is constructed in accordance with thepresent invention, the amount of force needed to complete the press-inprocess is greatly reduced, while the strength of the joint connectionremains virtually unchanged. Nevertheless, a very favorable retentioneffect and a firm press fit of the shaft in the base plate can beachieved, since a larger surplus can be used in the remaining jointsegments.

[0026] In accordance with the present invention, the notched shaft maybe made by being turned on a lathe, and is subsequently ground to sizewith a high degree of precision. Any existing chips or burrs in thetransition area between the outside diameter and the point of insertionmay be eliminated by a polishing process.

[0027] For the convenience of the reader, the above description hasfocused on a representative sample of all possible embodiments, a samplethat teaches the principles of the invention and conveys the best modecontemplated for carrying it out. The description has not attempted toexhaustively enumerate all possible variations. Other undescribedvariations or modifications may be possible. For example, where multiplealternative embodiments are described, in many cases it will be possibleto combine elements of different embodiments, or to combine elements ofthe embodiments described here with other modifications or variationsthat are not expressly described. Many of those undescribed variations,modifications and variations are within the literal scope of thefollowing claims, and others are equivalent.

The invention claimed is:
 1. A spindle motor for use in hard disk drivescomprising: a base plate; a shaft; a rotationally driven rotor; and abearing system rotationally supporting said rotationally driven rotor,wherein said shaft is fixedly mounted on said base plate, wherein saidbase plate comprises a hole for insertion of a portion of said shaft,said portion of said shaft and said hole defining a joint length l whensaid portion is pressed into said hole; and wherein said shaft furthercomprises at least one notch located along shaft's circumference andinterrupting said joint length l.
 2. The spindle motor according toclaim 1, wherein said hole further comprises an inner diameter, whereinsaid shaft further comprises an outer diameter, and wherein said outerdiameter of said shaft in the area of said notch is significantlysmaller than said inner diameter of said hole.
 3. The spindle motoraccording to claim 1, wherein said notch continues along at least halfof said joint length l.
 4. The spindle motor according to claim 2,wherein said notch continues along at least half of said joint length l.5. A hard disk drive having a spindle motor, said spindle motorcomprising: a base plate; a shaft; a rotationally driven rotor; and abearing system rotationally supporting said rotationally driven rotor,wherein said shaft is fixedly mounted on said base plate, wherein saidbase plate comprises a hole for insertion of a portion of said shaft,said portion of said shaft and said hole defining a joint length l whensaid portion is pressed into said hole; and wherein said shaft furthercomprises at least one notch located along shaft's circumference andinterrupting said joint length l.
 6. The hard disk drive according toclaim 1, wherein said hole further comprises an inner diameter, whereinsaid shaft further comprises an outer diameter, and wherein said outerdiameter of said shaft in the area of said notch is significantlysmaller than said inner diameter of said hole.
 7. The hard disk driveaccording to claim 1, wherein said notch continues along at least halfof said joint length l.
 8. The hard disk drive according to claim 2,wherein said notch continues along at least half of said joint length l.